This invention relates to instrumentation for measuring the performance of the heart's left ventricle. Such data has proven valuable in prognostic evaluation of cardiac cases.
The Ejection Fraction is the most important baseline measurement of the function of the left ventricle. One method of determining the Ejection Fraction is by cardiac catheterization. However, cardiac catheterization is an invasive technique, requires extensive dedicated space and equipment usually in a hospital setting, is time consuming, and has some inherent morbidity and mortality. Cardiac catheterization is also of no practical use during ambulatory examination due to the stationary nature of the data acquisition equipment.
Certain noninvasive methods, such as echo-cardiographic and radionuclide techniques, exist, but these procedures are inordinately expensive. Also, these procedures have limiting factors in ambulatory diagnosis or the collection of data outside of the dedicated cardiovascular environments.
Another noninvasive method of determining the Ejection Fraction, and hence left ventricular performance, is to collect a plurality of time-based measurements known as Systolic Time Intervals, or STI. The Ejection Fraction is a function of STI. The STI values are derived by first taking readings from arterial pulse tracing, phonocardiogram, and electrocardiogram (ECG) and then calculating STI. This method, while being relatively economical, is limited by the accuracy of the data received from currently used measuring devices, and moreover requires cumbersome post measurement computations that delay results. State-of-the-art techniques are not designed to allow readings in substantially real time, real time, or during ambulatory examination.
A definite need exists for a non-invasive, automated, real time method of, and apparatus for, making STI and EF measurements in an accurate, economical, and repeatable manner while the patient is either inactive or ambulatory. A need also exists for the collection of this data by a portable device outside of the hospital or physician's office.